Ni plating, particularly electroless Ni platings or deposits, enjoys technological applicability in various industries, such as the electronic, oil and gas, aerospace, machinery, automobile and magnetic recording media industries. Electroless Ni is employed in the metal finishing industry for various metal substrates, including steel, copper, Ni, aluminum and alloys thereof. Conventional electrolessly deposited Ni-phosphorous (P) platings exhibit desirable physical and chemical properties, such as hardness, lubricity, appearance, and corrosion resistance. An amorphous NiP plating is conventionally applied to a non-magnetic substrate, such as aluminum (Al) or an Al-alloy substrate in manufacturing magnetic recording media.
In operation, a magnetic disk is normally driven by the contact start-stop (CSS) method, wherein the head begins to slide against the surface of the disk as the disk begins to rotate and, upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducing head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head begins to slide against the surface of the disk again and eventually stops in contact with and pressing against the disk. Thus, each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk and stopping.
In order to achieve high areal density, it is considered necessary to minimize the flying height of the head above its associated recording surface. Thus, conventional textured substrates must be provided with an extremely smooth and defect free surface in order to achieve the requisite low flying height for high areal recording density. The absence of pits is especially important, since pits adversely affect magnetic recording.
It is recognized, however, that electroless metal plating, such as electroless Ni plating of a substrate, does not achieve a coating exhibiting a desired degree of surface smoothness, particularly the degree of smoothness necessary to satisfy the high areal recording density objectives of current magnetic recording media.
The continuing drive for higher areal recording density with an attendant reduction in the requisite flying height imposes greater requirements for surface smoothness. Market competitiveness further requires achievement of ultra-smooth electroless Ni coatings on non-magnetic substrates with increased manufacturing throughput and higher yield. Efforts to that end are constantly being evaluated. See, for example, Hajdu, J. B. et al., "THE ELECTROLESS NICKEL PROCESS FOR MEMORY DISKS", "The Electrochemically Society Magnetic Materials, Processes, and Devices", Electro Deposition Division Proceedings, Vol. 92-10, pages 39-55, 1992. In U.S. Pat. No. 5,141,778, it is disclosed that the introduction of cadmium ions in an electroless Ni plating bath enhances the surface smoothness of the deposited Ni coating. A strike bath was recommended in the plating process due to a shortened bath life due to the cadmium ions. Furthermore, the smoothing agents do not reduce the plating defects, such that no improvement of media yield was realized. Conventional methodology, however, has not been particularly successful in obtaining an electroless Ni coating exhibiting an average surface roughness (Ra) less than about 40 .ANG., particularly less than about 30 .ANG. if the as manufactured or as received blanks are rougher than 150 .ANG., when the roughness is measured by a TMS (Texture Measurement System) or a Tencor.
Accordingly, there exists a need for as-deposited ultra-smooth electrolessly deposited Ni coatings having reduced plating defects. There exists a particular need for methodology enabling the electroless deposition of amorphous NiP coatings on non-magnetic substrates, which coatings have an as-deposited Ra less than about 30 .ANG..